Telephones are now commonly provided with an adjustable stand to permit the user to adjust the tilt angle to a preferred viewing angle for reading the phone display (e.g. LCD display). This is beneficial from a visual perspective, but does not take into account the audio performance of the speakerphone. Typically, acoustical designers have relied on establishing an acceptable compromise between visual and audio considerations in selecting an industrial design for a set, or have tried to use adaptive filters to address audio performance issues. In the first case, only a compromise can be achieved. In the second case, adaptive filters are not always capable of obtaining enough information to provide the ideal correction to the audio signal. Moreover, adaptive filters have only been applied to the transmit signal of the set thus leaving the designer with only a compromise solution for optimizing the receive signal to the user.
Tilt sensors are known in the art of portable telephones to determine in which mode to operate a telephone. Colonna et al, in U.S. Pat. No. 6,115,620, disclose a mechanical switch that determines the position of the two parts of a portable telephone and based on this information permits a louder level of receive operation of the set. Lands and Banh, in U.S. Pat. No. 6,411,828, disclose the use of a gravitational sensor to perform the same function. Kielsnia, in U.S. Pat. No. 6,449,363, discloses a safety mechanism based on a tilt sensor that prevents a portable telephone from entering the speakerphone mode (i.e. louder receive signal) when the set is at an angle that would correspond to a user placing the set in handset mode. Martschink and Pai, in U.S. Pat. No. 6,510,326, disclose a tilt sensor that permits selecting the operational mode of a portable telephone dependant on its relation to an independent reference system (i.e. gravity). Martschink and Pai specifically set forth a telephone that switches between quiet and loud operation (i.e. substantially the same as handset and speakerphone modes) where, in the quiet (i.e. handset) mode, only the user can understand the receive signal. All of foregoing prior art relates to handheld telephones where only the receive volume is adjusted.